However, the chemical compound doesn't seem to help people lose pounds, and the preliminary study is so small that the findings could be misleading.

Still, it did "lower appetite and prevented weight gain in overweight people," said study co-author Gary Frost, chair of nutrition and dietetics at Imperial College London. "This is the first time that a food ingredient has been shown to decrease weight gain."

The ingredient in question contains propionate, a fatty acid that's created when fiber ferments in the colon.

Propionate "does a number of things in the body," Frost said. "It is used for energy by the colon and liver. It can be used to make glucose in the liver." And, he said, it appears to affect how much people eat by boosting signals that suppress appetite.

Fiber is considered an aid to digestion and is thought to help people feel full. But that's not certain, Frost said.

"There are lots of short-term studies that show fiber suppresses appetite but no long-term studies. We think that this is because the amount of fiber needed to be consumed to affect appetite in the long term is two to three times the current recommendation," he explained.

In the new study, researchers developed a chemical compound that includes propionate and gave it in fruit juice to half of 20 volunteers. The others got only inulin, a plant fiber.

The volunteers then got to eat as much as they wanted from a buffet. Those who'd consumed the propionate ate 14 percent less on average than others, the researchers said.

Then the researchers followed 49 overweight adults, ages 40 to 65, as they received either a propionate supplement or inulin alone and completed a six-month study.

Of the 25 who took the supplement, just one gained more than 3 percent of body weight, compared to six of the 24 who took inulin. Those who took the supplement also had less fat around their waists.